Method of Inter-RAT Bearer Change for 3GPP System

ABSTRACT

Methods and apparatus are provided for inter-RAT bearer change for the 3GPP network. In one novel aspect, a bearer termination procedure is performed upon detecting one or more triggering events for the inter-RAT bearer modification. In one embodiment, the UE established the 4G EPS bearer. The UE successfully performs a bearer change from 4G to 3G. Subsequently, the UE detects missing mandatory parameters during inter-RAT bearer change from 3G to 2G in an idle state. The UE performs bearer termination by releasing the PDP context. In one embodiment, the PDP context is locally released. In other embodiments, the UE explicitly releases bearer using the PDP context deactivation procedure. The locally released procedure can be triggered by the UE, or by the network, or by both the UE and the network. The explicitly PDP context release procedure can be triggered by the UE, or by the network, or by both the UE and the network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application No. 62/050,843, entitled, “Method of EnhancedBearer Continuity for 3GPP System Change” filed on Sep. 16, 2014; thesubject matter of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless communication,and, more particularly, to methods of enhanced bearer continuity for3GPP system change.

BACKGROUND

The wireless communications network has grown exponentially over theyears. A Long-Term Evolution (LTE) system offers high peak data rates,low latency, improved system capacity, and low operating cost resultingfrom simplified network architecture. LTE systems, also known as the 4Gsystem, also provide seamless integration to older wireless network,such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS).The 3^(rd) generation partner project (3GPP) network normally includes ahybrid of 2G/3G/4G systems. With the optimization of the network design,many improvements have developed over the evolution of variousstandards. In the 3GPP network where multiple radio access technology(RAT) systems are supported simultaneously, the UE may perform inter-RATchanges. Issues arise when mismatches are found among different systemssupported by the same network.

One of the problem is the inter-RAT bearer changes. In the LTE/4Gsystem, the activation of the EPS bearer has less mandatory parametersthan the 3G/2G PDP context. Upon inter-RAT bearer changes, if theoptional parameters are not presented in the EPS bearer, problems occursin the new PDP context set up because those parameters are mandatory forthe PDP context. In some scenarios, upon detecting the missing ofmandatory parameters, the inter-RAT bearer change is terminated. Inother scenarios, the behavior was not even defined.

Improvement and enhancement are required for inter-RAT bearer changeprocedures.

SUMMARY

Methods and apparatus are provided for enhanced bearer continuity forthe 3GPP network. In one novel aspect, the UE detects missing parametersfor the inter-RAT bearer change. The UE performs bearer preservationprocedures to maintain the bearer continuity. In one embodiment,predefined/preconfigured parameter settings are used. In anotherembodiment, the missing parameters are obtained from the network. In yetanother embodiment, signaling procedures are modified/designed to obtainthe missing parameters. In one embodiment, the predefined parameter setsare obtained locally from the UE. In another embodiment, mapping rulesare used to obtain the missing parameter by mapping the missingparameter with a value based on a known parameter. In one embodiment,the network provisionally configures the missing parameters upondetecting that multiple RATs are supported by the 3GPP network.Corresponding parameters are conditionally provisioned to the UE suchthat the bearer continuity can be maintained. In yet another embodiment,the Service Request procedure is used by the UE. The UE triggers theService Request procedure to request the missing parameters from thenetwork. In one embodiment, the triggering event is detecting aninter-RAT cell reselection. The one or more missing parameters areobtained using a network initiated PDP context modification procedurefor the 3G RAT, or the network initiated EPS bearer context modificationprocedure for the 4G RAT. In one embodiment, the MS-initiated PDPcontext modification procedure for the 3G RAT or the MS-initiated EPSbearer context modification procedure for the 4G RAT is used to obtainthe missing parameters from the network. In another embodiment, the RAUprocedure is used to obtain the missing parameters.

In another novel aspect, a bearer termination procedure is performedupon detecting one or more triggering events for the inter-RAT bearermodification. In one embodiment, the UE established the 4G EPS bearer.The UE successfully performs a bearer change from 4G to 3G.Subsequently, the UE detects missing mandatory parameters duringinter-RAT bearer change from 3G to 2G in an idle state. The UE performsbearer termination by releasing the PDP context.

In one embodiment, the PDP context is locally released. In otherembodiments, the UE explicitly releases bearer using the PDP contextdeactivation procedure. The locally released procedure can be triggeredby the UE, or by the network, or by both the UE and the network. Theexplicitly PDP context release procedure can be triggered by the UE, orby the network, or by both the UE and the network.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 illustrates an exemplary 3GPP wireless network with enhancedbearer continuity for 3GPP system change in accordance with embodimentsof the current invention.

FIG. 2 illustrates an exemplary detailed diagram in a 3GPP wirelessnetwork when mandatory IEs/parameters are missing during inter-RATbearer change in accordance with embodiments of the current invention.

FIG. 3 illustrates an exemplary flow diagram for the top-level bearerpreservation procedure for inter-RAT bearer change in accordance withembodiments of the current invention.

FIG. 4 illustrates an exemplary flow diagram for different embodimentsof the predefined/preconfigured procedure in accordance with embodimentsof the current invention.

FIG. 5 shows an exemplary diagram for multiple wireless communicationsdevices to send the corresponding responding frames concurrently overmore than one transmission instances and at least one transmissioninstance has less than the maximum allowed wireless communicationsdevices in accordance with embodiments of the current invention.

FIG. 6 illustrates an exemplary flow diagram of the Service Requestbased solution in accordance with embodiments of the current invention.

FIG. 7A illustrates UE Requested Bearer Resource Modification Procedurebased solution in accordance with embodiments of the current invention.

FIG. 7B illustrates MS-initiated PDP Context Modification Procedurebased solution in accordance with embodiments of the current invention.

FIG. 8A illustrates the first RAU based solution in accordance withembodiments of the current invention.

FIG. 8B illustrates the second RAU based solution in accordance withembodiments of the current invention.

FIG. 9 illustrates an exemplary flow chart for the bearer preservationprocedures during inter-RAT bearer change in accordance with embodimentsof the current inventions.

FIG. 10 illustrates an exemplary diagram of the bearer terminationsolution for inter-RAT bearer change in accordance with embodiments ofthe current invention.

FIG. 11 illustrates an exemplary flow chart of the local releaseprocedure for the inter-RAT bearer change in accordance with embodimentsof the current invention.

FIG. 12 illustrates an exemplary flow chart for the bearer terminationprocedures during inter-RAT bearer change in accordance with embodimentsof the current inventions.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates an exemplary 3GPP wireless network 100 with enhancedbearer continuity for 3GPP system change in accordance with embodimentsof the current invention. 3GPP system 100 supports one or more wirelessradio network access (RAT) networks, such a 4G/LTE system, a 3G systemand a 2G system. Each of the 3GPP system has a fixed base infrastructureunit, such as wireless communications stations 102 103, and 104, formingwireless networks distributed over a geographical region. The base unitmay also be referred to as an access point, an access terminal, a basestation, a Node-B, an eNode-B, or by other terminology used in the art.Each of the receiving wireless communications stations 102, 103, and 104serves a geographic area. A 4G/LTE system has a evolved node-B (eNB) 102connecting with a system architecture evolution (SAE) gateway 105, whichincludes the serving gateway (S-GW) and the packet data network (PDN)gateway (P-GW) via the S1 interface. A 3G system has a node-B 103 and aradio network controller (RNC). The RNC of the 3G system connects viathe lu interface with a serving GPRS support node (SGSN) 106, which isconnected to SAE gateway 106. A 2G system has a base transceiver station(BTS) 104 and a base station controller (BSC). The BSC of the 2G systemconnects with SGSN 106 via the Gb interface.

A wireless communications device/user equipment (UE) 101 in 3GPPwireless network 100 can be served by eNB 102, or by node-B 103 or byBTS/BSC 104. UE 101 establishes a bearer with 3GPP system 100. UE 101establishes EPS bearer in the 4G system via the S1 interface, orestablishes a PDP context in the 3G system via the lu interface, orestablishes a PDP context in the 2G system via the Gb interface. When UE101 is served in a 3GPP system that supports multiple RATs, UE 101 mayneed to perform inter-RAT bearer change. Different RATs are configuredwith different parameters for bearer activation. For example, for theEPS bearer established in the 4G system, several parameters are optionalas shown in a parameter set 111. The transaction identifier (TI), whichis used in both the 2G and the 3G system, is optional for the EPS bearersetup in the 4G/LTE system. The negotiated QoS (R99 QoS), which is usedin both 2G and 3G systems, is also optional for the EPS bearer.Similarly, the negotiated LLC SAPI and the radio priority, which areboth used in the 2G system, are both optional for the 4G EPS beareractivation. Therefore, it is possible that when the EPS bearer isactivated in the 4G/LTE system, one or more of the parameters, the TI,the R99 QoS, the LLC SAPI, and the radio priority, are omitted. If thebearer is first established in the 3G or 2G system, the above parametersincluding TI, the R99 QoS, the LLC SAPI, and the radio priority, are allmandatory. However, if a bearer is changed from a 4G system to a 3Gsystem, the parameters of the LLC SAPI and the radio priority isoptional. Therefore, a 3G transferred bearer parameter set 112 has theLLC SAPI, and the radio priority as optional. It is possible that when aPDP context is activated in the 3G system via bearer change from the 4Gsystem, one or more of the parameters of the LLC SAPI and the radiopriority is omitted. A parameter set 113 of the 2G system has allparameters listed as mandatory including the TI, the R99 QoS, the LLCSAPI, and the radio priority.

In one novel aspect, UE 101 performs a bearer preservation procedure tomaintain the continuity of the bearer for inter-RAT bearer change. Inone embodiment, the bearer preservation procedure is performed if one ormore mandatory parameters are missing when the UE changes bearer fromthe 4G system to the 3G system, or when the UE changes bearer from the4G system to the 2G system. In yet another embodiment, when the UEchanges from the 4G system to the 3G system omitting at least oneparameter including the LLC SAPI and the radio priority, the bearerpreservation procedure is performed when subsequently, the UE changesfrom the 3G to the 2G system.

In another novel aspect, the UE performs the bearer terminationprocedure when the UE changes from the 4G system to the 3G systemomitting at least one parameter including the LLC SAPI and the radiopriority and subsequently changes from the 3G to the 2G system. Thebearer termination procedure is performed either through local releaseof the PDP context or through the explicit PDP context deactivationprocedure.

FIG. 1 further shows simplified block diagrams of UE 101 and eNB 102 inaccordance with the current invention. The block diagram of eNB 102 isalso applicable to node-B 103 in the 3G system or the BTS/BSC 104 in the2G system.

eNB 102 has an antenna 126, which transmits and receives radio signals.A RF transceiver module 123, coupled with the antenna, receives RFsignals from antenna 126, converts them to baseband signals and sendsthem to processor 122. RF transceiver 123 also converts receivedbaseband signals from processor 122, converts them to RF signals, andsends out to antenna 126. Processor 122 processes the received basebandsignals and invokes different functional modules to perform features inbase station 102. Memory 121 stores program instructions and data 124 tocontrol the operations of base station 102. Base station 102 alsoincludes a set of control modules, such as inter-RAT bearer handler 125that carry out functional tasks for enhanced bearer continuity featuresin the 3GPP network.

UE 101 has an antenna 135, which transmits and receives radio signals. ARF transceiver module 134, coupled with the antenna, receives RF signalsfrom antenna 135, converts them to baseband signals and sends them toprocessor 132. RF transceiver 134 also converts received basebandsignals from processor 132, converts them to RF signals, and sends outto antenna 135. Processor 132 processes the received baseband signalsand invokes different functional modules to perform features in mobilestation 101. Memory 131 stores program instructions and data 136 tocontrol the operations of mobile station 101.

UE 101 also includes a set of control modules that carry out functionaltasks. An EPS bearer handler 191 establishes a 4G bearer connection inthe 3GPP system. A mandatory parameter handler 192 determines whetherone or more mandatory parameters are missing for an inter-RAT change ofbearer. A bearer preservation handler 193 maintains the bearercontinuity of the bearer for the inter-RAT change of bearer. A bearertermination handler 194 releases a PDP context upon detecting one ormore predefined conditions. An inter-RAT bearer handler 195 that handlesinter-RAT bearer changes, such as performs an inter-RAT bearer changefrom a 4G system to a 3G system and subsequently attempts an inter-RATbearer change from the 3G system to a 2G system in an idle state.

FIG. 2 illustrates an exemplary detailed diagram in a 3GPP wirelessnetwork when mandatory IEs/parameters are missing during inter-RATbearer change in accordance with embodiments of the current invention.In the first scenario, the EPS bearer is first activated in the 4Gsystem. An inter-RAT bearer change is attempted to change the bearer tothe 3G system. A parameter set 211 for the 4G system has fourparameters, the TI, the R99 QoS, the LLC SAPI, and the radio priority,all being optional. To transfer the bearer to the 3G system, parameterset 212 for the 3G system requires the TI and the R99 QoS to bemandatory while having the LLC SAPI, and the radio priority as optional.Therefore, in the inter-RAT bearer change procedure, the UE may detectmissing parameters/missing IEs if 4G parameter set 211 does not includeany one of the optional parameters of the TI and the R99 QoS. If themissing parameter is detected, a bearer preservation procedure isperformed to keep the bearer continuity.

Similarly, in the second scenario, the EPS bearer is first activated inthe 4G system. An inter-RAT bearer change is attempted to change thebearer to the 2G system. A parameter set 221 for the 4G system has fourparameters, the TI, the R99 QoS, the LLC SAPI, and the radio priority,all being optional. To transfer the bearer to the 2G system, parameterset 222 for the 2G system requires all four parameters the TI, the R99QoS, the LLC SAPI, and the radio priority to be mandatory. Therefore, inthe inter-RAT bearer change procedure, the UE may detect missingparameters/missing IEs if 4G parameter set 221 does not include any oneof the optional parameters of the TI, the R99 QoS, the LLC SAPI, and theradio priority. If the missing parameter is detected, a bearerpreservation procedure is performed to keep the bearer continuity.

In a third scenario, the UE successfully transfers the bearer from the4G system to the 3G system with the 4G parameter set 231 having both theTI and the R99 QoS as required by the 3G parameter set 232. Parameterset 231 may not include one or both of the optional parameters of theLLC SAPI, and the radio priority. Therefore, the transferred bearer maynot include one or both of the optional parameters of the LLC SAPI, andthe radio priority. Subsequently, the UE performs inter-RAT change fromthe 3G system to the 2G system in an idle state, which has a 2Gparameter set of 233 requiring all four parameters, the TI, the R99 QoS,the LLC SAPI, and the radio priority, as mandatory. In one novel aspect,upon detecting missing one or both the optional parameters/IEs of theLLC SAPI, and the radio priority, the UE performs the bearerpreservation procedure. In another novel aspect, upon detecting missingone or both the optional parameters/IEs of the LLC SAPI, and the radiopriority, the UE performs the bearer termination procedure.

In one novel aspect, upon detecting missing mandatory parameters duringinter-RAT bearer change, the UE performs the bearer preservationprocedure. In one embodiment, predefined/preconfigured parametersettings are used. In another embodiment, the missing parameters areobtained from the network. In yet another embodiment, signalingprocedures are modified/designed to obtain the missing parameters. Thefollowing figures further illustrates in details of differentembodiments of the bearer preservation procedure.

FIG. 3 illustrates an exemplary flow diagram for the top-level bearerpreservation procedure for inter-RAT bearer change in accordance withembodiments of the current invention. At step 301, the UE establishesthe 4G EPS bearer. At step 302, the UE prepares the inter-RAT bearerchange. At step 303, the UE determines whether there are missingmandatory parameters for the inter-RAT bearer change. If step 303determines no, the UE moves to step 304 and performs the bearer change.If step 303 determines yes, the UE moves to step 305 and performs abearer preservation procedure. The bearer preservation procedureincludes a predefined/preconfigured mandatory parameters procedure 311,an obtain-parameters from the network procedure 312, a signalingprocedure 313, and a hybrid procedure 314. There are differentembodiments of the different procedures.

FIG. 4 illustrates an exemplary flow diagram for different embodimentsof the predefined/preconfigured procedure 311 in accordance withembodiments of the current invention. In one embodiment, the UE and thenetwork can apply a preconfigured parameter setting in the 4G or 3Gnetwork. At step 411, the UE attempts to retrieve parameters locallythrough a database 412 upon detecting one or more missing parametersduring the inter-RAT bearer change. For example, when the UE changes toa 2G system, it detects the LLC SAPI is not presented or the LLC SAPI isset to be “LLC SAPI not assigned.” The UE can accesspreconfigured/predefined database 412 and retrieves the preconfiguredvalue for the LLC SAPI such the new bearer can be established.Similarly, if the radio priority parameter is not presented, the UEretrieves the preconfigured/predefined radio priority value fromdatabase 412.

In a different embodiment, the missing parameter is dynamically mappedbased on other parameters available. At step 421, the UE upon detectingmissing one or more mandatory parameters, retrieves such parametersusing predefined/preconfigured mapping rules 422. For example, rule 422includes mapping rules for LLC SAPI and radio priority. The UE upondetermining that one or both of the parameters of LLC SAPI and radiopriority are missing, the UE obtains a known parameter, such as thedelay class first. The UE subsequently uses mapping rules 422 toretrieve the missing parameters. For example, a mapping table for thedelay class the LLC SAPI is preconfigured in 422. The UE firstdetermines its current configured delay class. The UE subsequently usesthe mapping table to get the LLC SAPI value based on the delay class.Similarly, the UE can get the radio priority value by using the mappingtable of the delay class and the radio priority. Using the mapping ruleprocedure, the UE can get the most updated parameter based on its latestknown parameters. Other mapping table based on other known parameterscan be used. The mapping table itself can be preconfigured/predefinedand can be updated dynamically through system signaling or other means.

In another embodiment, the missing parameters can be obtained throughprovisioning from the network. FIG. 5 illustrates obtaining missingparameters from network provisioning. For example, in the 4G system, theparameters the TI, the R99 QoS, the LLC SAPI, and the radio priority,should be conditionally provided if the operator/PLMN also supports the2G system. Similarly, the parameters TI, the R99 QoS, should beconditionally provided if the operator/PLMN also supports the 3G system.In another example, in the 3G system, if the 2G system is alsosupported, the parameters of the LLC SAPI, and the radio priority,should be conditionally provided. At step 511, the UE establishes the 4GEPS bearer. At step 512, the UE checks if the 3GPP network alsosupported the 2G network. If step 512 determines yes, the UE obtainsconditionally configured parameters of the TI, the R99 QoS, the LLCSAPI, and the radio priority from the network. If step 512 determinesno, the UE moves to step 513 and determines if the 3G system is alsosupported. If step 513 determines yes, the UE obtains conditionallyconfigured parameters of the TI and the R99 QoS, from the network.Otherwise, there is no additional parameter needed.

Similarly, at step 521, the UE establishes the 3G PDP context. At step522, the UE checks if the 3GPP network also supported the 2G network. Ifstep 512 determines yes, the UE obtains conditionally configuredparameters of the TI, the R99 QoS, the LLC SAPI, and the radio priorityfrom the network. Otherwise, there is no additional parameter needed.

In other embodiments, signaling procedures are used for bearerpreservation procedures including Service Request based solution,MS-initiated PDP Context Modification Procedure/UE Requested BearerResource Modification Procedure, and the Routing Area Update procedurebased solution.

FIG. 6 illustrates an exemplary flow diagram of the Service Requestbased solution in accordance with embodiments of the current invention.A UE 601 is connected with a 3GPP network 602. In 3G RAT, UE 601 can tryto send SERVICE REQUEST (service type==Data) to hint the network totrigger network initiated allocation of the 2G parameters, such as theLLC SAPI value and the Radio Priority value, assigned to the UE. In 4GRAT, UE 601 can try to send SERVICE REQUEST with additional EPS bearercontext-status parameters to hint the network to trigger networkinitiated allocation of 3G or 2G parameters, such as the LLC SAPI valueand the Radio Priority value, assigned to the UE. The SERVICE REQUESTmessage can be sent before cell reselection procedure. In oneembodiment, the SERVICE REQUEST message can be triggered based on thetype of the cell-reselection, including intra-frequency, inter-frequencyand inter-RAT. In one embodiment, the Service-Request based solution istriggered upon detecting the inter-RAT cell reselection, while not forother types of the cell reselection. In yet another embodiment, aftersending the SERVICE REQUEST message, the UE may suspend the cellreselection procedure and wait for the network allocated parameter for aperiod before performing the cell reselection.

As shown in FIG. 6, at step 611, UE 601 sends a SERVICE REQUEST to 3GPPnetwork 602. At step 612, UE 601 suspends the cell reselection procedurefor a period such the network allocated parameters can be retrieved. Atstep 613, the UE performs the network initiated PDP Context ModificationProcedure if the bearer is in the 3G RAT. If the bearer is in the 4GRAT, UE 601 performs the network initiated EPS bearer ContextModification Procedure. At step 614, UE 601 obtains the missingmandatory parameters/IEs from the network.

In other embodiments, UE Requested Bearer Resource ModificationProcedure based solution for 4G RAT, or MS-initiated PDP ContextModification Procedure based solution for 3G RAT are used to retrievemissing parameters. In 4G RAT, the UE can trigger the “UE RequestedBearer Resource Modification Procedure” to trigger the network to assignvalid parameters (e.g., LLC SAPI value and Radio Priority value) in the“MODIFY EPS BEARER CONTEXT REQUEST (Network to MS direction)” message.In 2G or 3G RAT, the UE can trigger the “MS-Initiated PDP ContextModification Procedure” to trigger the network to assign validparameters (e.g., LLC SAPI value and Radio Priority value) in the“MODIFY PDP CONTEXT ACCEPT (Network to MS direction)” message. In2G/3G/4G RAT, it can be specified that the network sends the “MODIFY PDPCONTEXT REQUEST (Network to MS direction)” or “MODIFY EPS BEARER CONTEXTREQUEST” messages for parameters allocation. In one embodiment, bearermodification procedures can be triggered before cell reselectionprocedure. In other embodiments, after triggering the bearermodification procedures, the UE may suspend the cell reselectionprocedure and wait for the network allocated parameter for a periodbefore performing the cell reselection.

FIG. 7A illustrates UE Requested Bearer Resource Modification Procedurebased solution in accordance with embodiments of the current invention.UE 701 connects with 4G network 702. At step 711, UE 701 triggers BearerResource Modification procedure. In one embodiment, at step 712, UE 701suspends the cell reselection procedure such that the missing parametersare obtained. At step 713, UE 701 receives Modify EPS Bearer ContextRequest from 4G network 702 with parameters, such as LLC SAPI and RadioPriority. At step 714, UE 701 obtains the one or more missingparameters/IEs.

FIG. 7B illustrates MS-initiated PDP Context Modification Procedurebased solution in accordance with embodiments of the current invention.UE 701 connects with 3G network 703. At step 721, UE 701 triggers PDPContext Modification procedure. In one embodiment, at step 722, UE 701suspends the cell reselection procedure such that the missing parametersare obtained. At step 723, UE 701 receives Modify PDP Context Acceptfrom the 3G network 703 with parameters, such as LLC SAPI and RadioPriority. At step 714, UE 701 obtains the one or more missingparameters/IEs.

In other embodiments, RAU based solution are used to enable bearercontinuity during inter-RAT bearer change. Upon system change to 2G from3G, the UE detects that it does not have valid LLC SAPI value (includingthe LLC SAPI is “LLC SAPI not assigned”) or the 2G Radio Priority valuefor the specific PDP context. In one embodiment, RAU process is used toretrieve the missing mandatory parameters/IEs. Different embodiments ofthe RAU based solution can be used and are illustrated below.

FIG. 8A illustrates the first RAU based solution in accordance withembodiments of the current invention. A UE 801 connects with a 3GPPnetwork 802. At step 811, UE 901 detects missing parameters/IEs duringinter-RAT bearer change. At step 812, UE 801 sends RAU REQUEST tonetwork 802 indicating the existence of the specific PDP context. Atstep 813, network 802 replies with an RAU_ACCEPT message foracknowledgement. At step 814, network 802 initiates aMODIFY_PDP_CONTEXT_REQUEST with a proper LLC SAPI value and a RadioPriority assigned to the specific PDP context. At step 815, UE 801replies a MODIFY_PDP_CONTEXT_ACCEPT for confirmation.

FIG. 8B illustrates the second RAU based solution in accordance withembodiments of the current invention. The second RAU based solution is avariation of the first RAU based solution. It covers different messagesequence of the method. A UE 801 connects with a 3GPP network 802. Atstep 811, UE 901 detects missing parameters/IEs during inter-RAT bearerchange. At step 812, UE 801 sends RAU REQUEST to network 802 indicatingthe existence of the specific PDP context. At step 813, network 802initiates a MODIFY_PDP_CONTEXT_REQUEST with a proper LLC SAPI value anda Radio Priority assigned to the specific PDP context. At step 814, UE801 replies a MODIFY_PDP_CONTEXT_ACCEPT for confirmation. At step 815,network 802 replies with an RAU_ACCEPT message for acknowledgement.

In other embodiment using bearer preservation procedures, hybridsolutions can be used by mixing different solutions mentioned above,including the pre-defined/preconfigured parameter settings, the networkprovisioning solution, the service request based solution, theMS-initiated signaling solution and the RAU based solution. The hybridsolution may use the combination of a plurality of the above solutionsto obtain the missing parameter(s). It can use different solutions fordifferent parameters, or use different solutions based on differenttriggering events or during different conditions. For example, somemandatory parameters are provisioned from the network while the othermandatory parameters are obtained by the pre-defined mapping rule. Inanother example, some mandatory parameters are obtained by thepre-configured values while the other mandatory parameters are obtainedby the pre-defined mapping rule. Other combinations of the hybridsolution are supported to optimize further the performance or efficiencyof the network.

FIG. 9 illustrates an exemplary flow chart for the bearer preservationprocedures during inter-RAT bearer change in accordance with embodimentsof the current inventions. At step 901, the UE establishes an EPS bearerin a 3GPP system, wherein the 3GPP system includes 2G, 3G, and 4G RAT.At step 902, the UE detects one or more mandatory parameters missingduring an inter-RAT change of the bearer. At step 903, the UE performs abearer preservation procedure upon detecting the one or more missingmandatory parameters, wherein the bearer preservation proceduremaintains a continuity of the bearer for the inter-RAT change.

In another novel aspect, the UE performs a bearer termination upondetecting one or more predefined/preconfigured conditions. In oneembodiment, the UE established the 4G EPS bearer. The UE successfullyperforms a bearer change from 4G to 3G. Subsequently, the UE detectsmissing mandatory parameters during inter-RAT bearer change from 3G to2G in an idle state. The UE performs bearer termination by releasing thePDP context.

FIG. 10 illustrates an exemplary diagram of the bearer terminationsolution for inter-RAT bearer change in accordance with embodiments ofthe current invention. At step 1001, the UE establishes the 4G EPSbearer. At step 1002, the UE changes to 3G bearer successfully. At step1003, the UE determines if there are missing mandatory parameters inpreparation to change to the 2G bearer. If step 1003 determines no, theUE moves to step 1004 and changes to 2G bearer. If step 1003 determinesyes, the UE moves to step 1005 and performs bearer terminationprocedure. In some embodiments, the UE terminates the bearer usinglocally releasing of the specific 3G PDP context at step 1011. In otherembodiments, the UE explicitly releases bearer using the PDP contextdeactivation procedure at step 1012.

In one embodiment, the locally releasing procedure can be initiated bythe UE. In other embodiments, the locally releasing procedure isinitiated by the network or by both the network and the UE. In oneembodiment, the locally releasing procedure involves locally clearing ofcorresponding context of the bearer. For example, internal entities ofthe UE, such as the session management layer (SM), the subnetworkdependent convergence protocol (SNDCP), the logic link control layer(LLC), the radio link control layer (RLC) and the radio access bearermanager (RABM), will start to clear the corresponding context for thebearer/PDP context. In another embodiment, if the UE is in the “LLC ACKmode,” the LLC layer needs to negotiate with the network to finish thelocal release procedure. Other internal releasing procedure can beemployed to release the PDP context locally upon detecting the missingof mandatory parameters/IEs. After locally releasing the PDP context,the UE may notify the operating system, such as the Android, about thePDP context release event. Subsequently, the OS will determine whetherit needs to re-establish the PDP context. At the same time, themodem/network may try to synchronize with the PDP context status upondetecting one or more triggering events. The triggering events includes,the Mobility Management layer (MM) triggers RAU/TAU (Tracking AreaUpdate) procedure to sync up PDP context information with the network;MO or MT detach procedure; User/operating system re-establishes the PDPcontext by using the same NSAPI/TI values. The network should accept thenew setup PDP context and release the old one. In another embodiment,the network actively release the PDP context by triggering MT deactivateor MT modify procedure for the PDP context just been released.

In other embodiments, the explicitly releases bearer procedure can beinitiated by the UE, or by the network, or by both the UE and thenetwork. The standard PDP context deactivation procedures are followed.

FIG. 11 illustrates an exemplary flow chart of the local releaseprocedure for the inter-RAT bearer change in accordance with embodimentsof the current invention. A UE 1101 is connected with a 3GPP network1102. At step 1111, UE 1101 locally releases the PDP context. At step1112, UE 1101 clears the internal corresponding context with eachinternal modules, such as the SM, the SNDCP, the LLC, the RLC, and theRABM. At step 1113, upon completing the local PDP context release, UE1101 notifies the operating system (OS). Optionally at step 1114, the OSdetermines whether to re-establish the PDP context. At step 1121, UE1101 monitors sync-up triggering events. The sync-up triggering eventsincludes predefined conditions in 1122. At step 1123, upon detecting oneor more sync-up triggering events, UE 1101 performs sync-up procedurewith 3GPP network 1102.

FIG. 12 illustrates an exemplary flow chart for the bearer terminationprocedures during inter-RAT bearer change in accordance with embodimentsof the current inventions. At step 1201, the UE establishes an EPSbearer in a 3GPP system, wherein the 3GPP system includes 2G, 3G, and 4GRAT. At step 1202, the UE performs an inter-RAT bearer change from a 4Gsystem to a 3G system. At step 1203, the UE subsequently, attempts aninter-RAT bearer change from the 3G system to a 2G system in an idlestate. At step 1204, the UE detects one or more mandatory parametersmissing during the inter-RAT change of the bearer. At step 1205, the UEperforms a bearer termination by releasing a Packet Data Protocol (PDP)context.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method, comprising: establishing an EvolvedPacket System (EPS) bearer by a user equipment (UE) in a 3^(rd)Generation Partnership Project (3GPP) system, wherein the 3GPP systemincludes 2G, 3G and 4G radio access technologies (RAT); performing aninter-RAT bearer change from a 4G system to a 3G system; subsequently,attempting an inter-RAT bearer change from the 3G system to a 2G systemin an idle state; detecting one or more mandatory parameters missingduring the inter-RAT change of the bearer; and performing a bearertermination by releasing a Packet Data Protocol (PDP) context.
 2. Themethod of claim 1, wherein the missing parameters include: a logic linkcontrol (LLC) service access point identifier (SAPI) and a 2G radiopriority value.
 3. The method of claim 1, wherein the PDP context islocally released.
 4. The method of claim 3, wherein the local release ofthe PDP context is triggered by one local release triggers comprising:the UE, a network entity, and both the UE and a network entity.
 5. Themethod of claim 3, further comprising: clearing internal correspondingcontext for the PDP bearer.
 6. The method of claim 3, furthercomprising: notifying an operating system of the UE of a completion ofthe local release of the PDP context for the bearer.
 7. The method ofclaim 3, further comprising: performing a sync-up procedure with the3GPP system upon detecting one or more sync-up triggering events.
 8. Themethod of claim 7, wherein the sync-up triggering events comprises: aMobility Management layer (MM) triggers Routing Area Update (RAU)procedure to sync up PDP context information with the network, a MMlayer triggers a TAU (Tracking Area Update) procedure to sync up PDPcontext information with the network, a mobile originated (MO) or mobileterminated (MT) detach procedure, and an operating system re-establishesthe PDP context by using the same NSAPI/TI values.
 9. The method ofclaim 1, wherein the PDP context is explicitly terminated by a PDPcontext deactivation procedure.
 10. The method of claim 9, wherein theexplicit termination of the PDP context is triggered by one terminationtriggers comprising: the UE, a network entity, and both the UE and anetwork entity.
 11. An apparatus, comprising: a transceiver thattransmits and receives radio signals via a radio access link; an evolvedpacket system (EPS) bearer handler that establishes a 4G bearerconnection in a 3^(rd) Generation Partnership Project (3GPP) system,wherein the 3GPP system includes 2G, 3G and 4G radio access technologies(RAT); an inter-RAT bearer handler that performs an inter-RAT bearerchange from a 4G system to a 3G system and subsequently attempts aninter-RAT bearer change from the 3G system to a 2G system in an idlestate; a mandatory parameter handler that determines whether one or moremandatory parameters are missing for an inter-RAT change of bearer; anda bearer termination handler that performing a bearer termination byreleasing a Packet Data Protocol (PDP) context.
 12. The apparatus ofclaim 11, wherein the missing parameters include: a logic link control(LLC) service access point identifier (SAPI) and a 2G radio priorityvalue.
 13. The apparatus of claim 11, wherein the PDP context is locallyreleased.
 14. The apparatus of claim 13, wherein the local release ofthe PDP context is triggered by one local release triggers comprising:the UE, a network entity, and both the UE and a network entity.
 15. Theapparatus of claim 13, further comprising: an internal context handlerthat clears internal corresponding context for the PDP bearer.
 16. Theapparatus of claim 13, further comprising: an operating system (OS)handler that notifies an OS of the UE of a completion of the localrelease of the PDP context for the bearer.
 17. The apparatus of claim13, further comprising: a sync-up handler that performs a sync-upprocedure with the 3GPP system upon detecting one or more sync-uptriggering events.
 18. The apparatus of claim 17, wherein the sync-uptriggering events comprises: a Mobility Management layer (MM) triggersRouting Area Update (RAU) procedure to sync up PDP context informationwith the network, a MM layer triggers a TAU (Tracking Area Update)procedure to sync up PDP context information with the network, a mobileoriginated (MO) or mobile terminated (MT) detach procedure, and anoperating system re-establishes the PDP context by using the sameNSAPI/TI values.
 19. The apparatus of claim 11, wherein the PDP contextis explicitly terminated by a PDP context deactivation procedure. 20.The apparatus of claim 11, wherein the explicit termination of the PDPcontext is triggered by one termination triggers comprising: the UE, anetwork entity, and both the UE and a network entity.